That depends on what train your reservation is for and where you booked it.

Thanks for letting me know!

Looking at it now, the train from Vienna to Munich is non-refundable, but the train from Munich to Paris is non-refundable.

I want to come to Paris from Salzburg at the risk of even a little damage, but if I don't cancel the train from Vienna to Munich, will I be spending a day's worth of pass?

I don't know how to cancel the ticket:(

Do you want to cancel a travel day or a seat reservation?

Travel days can be cancelled in the Railplanner until 23.59 CET the day before. 

Travel days should not be activated in advance, but just before boarding the first train of the day. 

You mean the latter one is refundable? If it's the direct TGV then that should indeed be the case. You can get a refund from the place where you booked it.

Reservations are not linked to your pass. You can cancel travel days if you go to My Pass, select the travel day and then tap on "Cancel travel day”. Please do that for all your travel days and then also cancel the activation of your pass. It's not a good idea to activate your pass or a travel day in advance.

Then can I register my travel day the day before I take the train for each travel day?

Sure you can. That's the best way to do it. It's like using the paper pass: you'd never fill the dates out in advance.